The modular nature of eukaryotic activator proteinsgave scientists an idea for a way to find proteins thatinteract with any particular protein of interest. Theidea is to use the protein–protein interaction to bringtogether a DNA-binding region with an activation region, creating an artificial activator that consists oftwo polypeptides held together noncovalently by theinteraction.The method is called the yeast two-hybrid system,and it has three components. First, the yeast contains areporter gene construct in which UASG (an enhancerlike sequence that binds the activator Gal4 as describedin Problem 8) drives the expression of an E. coli lacZreporter (encoding the enzyme ß-galactosidase) from ayeast promoter. Second, the yeast also expresses a fusion protein in which the DNA-binding domain of Gal4is fused to the protein of interest; this fusion protein iscalled the bait. The third component is a cDNA librarymade in plasmids, where each cDNA is fused in frameto the activation domain of Gal4, and these can beexpressed in yeast cells as prey fusion proteins.How could you use a yeast strain containing thefirst two components, along with the plasmid cDNAexpression library described, to identify prey proteinsthat bind to the bait protein? How is this procedurerelevant to the goal of finding proteins that might interact with each other in the cell?
The modular nature of eukaryotic activator proteins
gave scientists an idea for a way to find proteins that
interact with any particular protein of interest. The
idea is to use the protein–protein interaction to bring
together a DNA-binding region with an activation region, creating an artificial activator that consists of
two polypeptides held together noncovalently by the
interaction.
The method is called the yeast two-hybrid system,
and it has three components. First, the yeast contains a
reporter gene construct in which UASG (an enhancerlike sequence that binds the activator Gal4 as described
in Problem 8) drives the expression of an E. coli lacZ
reporter (encoding the enzyme ß-galactosidase) from a
yeast promoter. Second, the yeast also expresses a fusion protein in which the DNA-binding domain of Gal4
is fused to the protein of interest; this fusion protein is
called the bait. The third component is a cDNA librarymade in plasmids, where each cDNA is fused in frame
to the activation domain of Gal4, and these can be
expressed in yeast cells as prey fusion proteins.
How could you use a yeast strain containing the
first two components, along with the plasmid cDNA
expression library described, to identify prey proteins
that bind to the bait protein? How is this procedure
relevant to the goal of finding proteins that might interact with each other in the cell?
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